Such a front jaw is already described in the EP-A1 0 311 832 (corresponds to U.S. Pat. No. 4,902,031). The release force of a sole holder half is increased due to the friction between the ski boot and the ski, which release force is further compounded in this front jaw in the case of a twisting fall, and even further when combined with a frontal fall, so that in this case the actual release force remains approximately constant.
The axis of the release spring or the pull rod extends in this embodiment (see FIGS. 3 to 5) at an acute angle with respect to the upper side of the ski. This, however, has the result that only one component of the force of the release spring acts parallel with respect to the upper side of the ski. It is only this component that is effective for holding the ski boot. However, it was earlier determined that in order to achieve the requisite holding force, a stronger spring must be used. Because of the inclined position of the pull rod also further structural parts of the front jaw are arranged inclined, thus making the manufacture and the design more difficult.
In another known front jaw according to AT-PS 321 170 (corresponds to U.S. Pat. No. 3,902,730), the two toggle levers grip only the laterally facing edges of the sole of the boot. Furthermore, the pull rod has at its rear end a cross-part which, in the skiing position of the front jaw, rests on the shorter lever arms of the two toggle levers. To hold the sole of the boot from above, an additional sole down-holding means is provided, which during a backward twisting fall of the skier can be pivoted upwardly about an axis supported in the housing. Because of the additional sole down-holding means, this front jaw is slightly complicated in its design.
According to a presently pending application Ser. No. 07/556 845, filed Jul. 23, 1990, assigned to the same assignee as in the present matter, a front jaw has already been suggested in which the two toggle levers are supported in a bearing part arranged at the rear end of a housing, which bearing part is pressed against the housing under the influence of a release spring. The ski boot in this design is held exclusively by the two toggle levers, and the bearing part can during a fall of the skier be pivoted upwardly in the longitudinal plane and furthermore in a transverse plane. However, this front jaw has an automatic adjustment of the two toggle levers to the thickness of the sole of the boot, which is caused by two inclined surfaces and the release spring. The initial tension of the release spring is thereby, even if to a limited degree, dependent on the thickness of the sole of the boot.